FX has Gradient stroke (non-uniform) as well by the way. Try select the area with marquee (M) or (w) then Edit>Stroke should become available. Or make sure your layer is not locked. Though you can only do solid line with this!
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Hasan SahogluMar 7 '12 at 14:43

have another idea! you can manually draw a selection (M or L) around your shape and paint! Its not very straight forward but it would work.
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Hasan SahogluMar 7 '12 at 15:06